Three T-even phage-induced enzymes involved directly or indirectly in the formation of thymidine 5'-monophosphate, deoxycytidylate deaminase, thymidylate synthetase and deoxycytidine triphosphatase are under investigation. Amino acid sequence studies have been initiated already with homogeneous deoxcytidylate deaminase and the following studies are planned: (1) the relationship of enzyme activity to binding properties of the enzyme, particularly with respect to the substrate and allosteric effectors; (2) the influence of the allosteric effectors on enzyme conformation; (3) the determination of the similarity of the subunits through the use of such studies as endgroup and "fingerprint" analysis, the latter technique to be used in a comparison of the T2-induced deaminase with that of T4, T6 and chick embryo; (4) purification of the chick embryo deaminase to homogeneity with emphasis on the role of the regulatory ligands in reactivating inactive enzyme; (5) the mechanism of inactivation of the deaminase by the microsomal-disulfide interchange enzyme. The purification of thymidylte synthetase to homogeneity is well under way, which should provide material for a comparative analysis with those synthetases purified from other organisms. Studies on this enzyme will be concentrated on its subunit structure, mechanism of enzyme action, and irreversible inhibiton by 5-fluorodeoxyuridylate. With the use of a new spectrophotometric assay, the extensive purification of deoxycytidine triphosphatase will be pursued and its interaction with the above enzymes will be investigated. Aside from assessing the influence of regulatory agents on enzyme activity, those agents affecting the temporal order of genetic expression of the above enzymes, in addition to several other DNA related enzymes will be investigated both in vivo and in vitro. These studies will hopefully provide an insight into the concept of allosteric regulation, as well as a delineation of those forces affecting the transcription and translation of enzymes related to DNA synthesis.